The janitor doesn't look too beat down to me, but I don't imagine Rockwell painting him that way.
Harder for me to see the skill in the shark, because I don't play with Photoshop-like programs. For all I know one could just scan a photo of and do minimal touch-up. Moving images that one can't just film and fool a little with - I can understand the skill there.
The shark wasn't done in photoshop, it was created in Maya, a 3d graphics program. It's the same program used to create the animation in Shrek, Monsters Inc, etc. Without getting too deep into it, he started by making a 3d wire frame shaped like a shark. He created joints and other "moveable" links to allow it to move fins, open and close it's mouth, etc. Then he selects a "skin" texture and applies that to the outside. Finally, he paints the surface of the skin to make it look like a shark. This was not done from a photo. It's a screen shot, but using the proper animation program, you can create a 3d movie of it swimming, with water surface reflections shimmering on it's back, and a good game programmer can make it controllable with a joystick. I'm probably prejudiced since he's my brother, but his talent blows me away. The advantage of this over a real shark is that this shark will take direction, and doesn't eat nearly as much.